1. Field of the Invention
This invention relates to a motor-driven power steering control apparatus assisting steering force by an electric motor. More particularly, the invention relates to a motor-driven power steering control apparatus for detecting overload of the electric motor without delay.
2. Description of Related Art
When a vehicle such as a car is stopped or running at a low speed, an enormous amount of power is required in order to operate the steering wheel. A power steering apparatus, assisting steering force with an electric motor in order to reduce steering force required for a driver, is well known. (Japanese Patent Application Laid-Open No. 60-35663)
The aforementioned electric motor is provided in a narrow space in an engine compartment in which heat is generated. The ambient temperature thereof is very high by calorification of an engine.
As explained above, the electric motor assisting steering force is frequently exposed to high temperature, as the working environment is not ideal. In such a working environment, in order not to burn the electric motor, the one whose output and application temperature has some tollerance may be used. But in that case, the electric motor itself is enlarged to require a wide fixing space, so it is impossible to fix, and results in great expense. Therefore, in the case where a small-sized electric motor is used, it is considered that current supply time to the motor and current value thereof are calculated and overload thereof is detected and the electric motor is protected. But, in this case, there is a problem that a difference of the detected overload occurs between initial driving and driving after a specified time of the electric motor. On the other hand, independently of the above case, it is considered that a temperature sensor for detecting the temperature of the electric motor is provided thereon, however, in this case, there is a problem that the overload state cannot be detected immediately and properly because of a delay of operation of the temperature sensor.